Filter-out deps of unsupported arch

When a common-arch module (ex: phony) has the "required" dependencies on
native modules (ex: cc_library), both 32 and 64-bit variants of the
native modules are added as dependencies. This by itself is fine and
actually is intended, otherwise there's no way for us to install both
arch variants via required deps.

However, this imposes a problem when the common-arch module is depended
on by a filesystem module with compile_multilib: "first". Here, the
expectation is that only the first variant (64-bit) of the native module
is instaled, but in reality both variants are installed.

To handle this situation, make sure that the packaging routine filters
out packaging specs from unsupported architecture.

Bug: N/A
Test: go test ./... under soong/filesyste

Change-Id: Ie1ad5ace2e5d88e00183a115f4a76e5df87a8166